Method of repairing a Ni-base alloy part

This is a Continuation Application of PCT Application No. PCT/JP02/05904, filed Jun. 13, 2002, which was not published under PCT Article 21(2) in English.

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-179052, filed Jun. 13, 2001, the entire contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to a method of repairing a Ni-based alloy part, and more particularly, to a method of repairing a Ni-based alloy part to be used in high-temperature components, specifically, components in such machines as gas turbines and jet engines, and more specifically, rotor blades and stator vanes.

2. Description of the Related Art

As is known well, rotor blades and stator vanes generally employ casting alloys. Of these alloys, in particular, Ni-based alloys are frequently used. Since Ni-based alloys have great flexible moldability, the parts made of Ni-based alloys may be easily manufactured and partially repaired.

FIG. 4 is a schematic view of a rotor blade 1 of a gas turbine and FIG. 5 is an enlarged sectional view of the damaged portion X shown in FIG. 4 . As shown in FIG. 5 , an undercoat layer 3 and a topcoat layer 4 formed of, for example, a ZrO 2 -based ceramic, are sequentially formed on a base material 2 . Part of the topcoat layer 4 is peeled off. The peeled-off portion is called a thermal barrier coating (TBC) peeled-off portion 5 . It should be noted that reference numeral 6 in FIG. 5 indicates a denatured portion of the surface of the undercoat layer 4 formed at a position corresponding to the peeled-off portion 5 , and reference numeral 7 indicates a damaged portion formed on the topcoat layer 4 around the peeled-off portion 5 .

Such a TBC peeled-off portion may possibly be repaired by the low-pressure plasma spray method. However, this method entails cleaning (by a reversed polarity arc) and preheating at a temperature exceeding 800° C. If the method is used for partial repair, the topcoat layer 4 may be damaged. For the reason, the plasma spray method is never employed.

Conventionally, a TBC peeled-off portion is repaired by entirely removing the topcoat layer 4 and undercoat layer 3 mechanically and chemically, followed by forming another undercoat layer by the low-pressure plasma spray method and another topcoat layer by the atmospheric-pressure plasma spray method or the like.

However, in such a conventional repairing method, even if the top coating layer 4 is only partially damaged, the entire rotor blade must be coated again, which increases the cost.

The present invention has been conceived taking the aforementioned circumstances into consideration. An object of the present invention is to provide a method of repairing a Ni-based alloy part, comprising: removing a damaged portion of a topcoat layer and the denatured portion of an undercoat layer corresponding to the damaged portion; forming another undercoat layer in the removed portion where the original undercoat layer has been removed by spraying performed in the atmosphere at a spray particle speed of 300 m/s or more and a base-material temperature of 300° C. or less; and forming another topcoat layer in the damaged portion of the topcoat layer, whereby the coat layers can be partially repaired, enabling cost reduction.

Another object of the present invention is to provide a method of repairing a Ni-based alloy part, comprising: removing a damaged portion of a topcoat layer and the denatured portion of an undercoat layer corresponding to the damaged portion; forming another undercoat layer in the removed portion where the original undercoat layer has been removed by spraying performed at reduced pressure, a spray particle speed of less than 300 m/s, and a base-material temperature of 600° C. or less; and forming another topcoat layer in the damaged portion of the topcoat layer, whereby the coat layers can be partially repaired, enabling cost reduction.

To attain the aforementioned objects, a method of repairing a Ni-based alloy part according to the present invention is employed. More specifically, there is provided a method of repairing a Ni-based alloy part having an undercoat layer and a topcoat layer stacked on a Ni-based alloy base when the topcoat layer is damaged, comprising the steps of: removing a damaged portion of the topcoat layer and a denatured portion of the undercoat layer corresponding to the damaged portion; forming another undercoat layer in the removed portion where the original undercoat layer has been removed by spraying performed in the atmosphere at a spray particle speed of 300 m/s or more and a base-material temperature of 300° C. or less; and forming another topcoat layer in the damaged portion of the topcoat layer.

Furthermore, the method of repairing a Ni-based alloy part according to the present invention is the one for repairing a Ni-based alloy part having an undercoat layer and a topcoat layer stacked on a Ni-based alloy base when the topcoat layer is damaged, comprising the steps of: removing a damaged portion of the topcoat layer and the denatured portion of the undercoat layer corresponding to the damaged portion; applying spraying to the removed portion where the undercoat layer has been removed, at reduced pressure, a spray particle speed of less than 300 m/s, and a base-material temperature of 600° C. or less; and forming another topcoat layer in the damaged portion of the topcoat layer.

FIGS. 1A to 1D illustrate a method of repairing a Ni-based alloy part according to Embodiment 1 of the present invention, in accordance with order of repairing steps;

FIGS. 2A to 2D illustrate a method of repairing a Ni-based alloy part according to Embodiment 2 of the present invention, in accordance with order of repairing steps;

FIGS. 3A to 3D illustrate a method of repairing a Ni-based alloy part according to Embodiment 3 of the present invention, in accordance with order of repairing steps;

FIG. 4 illustrates a rotor blade of a gas turbine having a damaged portion; and

FIG. 5 illustrates a conventional method of repairing a Ni-based alloy part.

The present invention will now be explained in detail, below.

In the first aspect of the invention, the spray particle speed is set at 300 m/s or more. This is because if the spray particle speed is less than 300 m/s, an oxide film is easily deposited on another undercoat layer to be formed where the original undercoat layer has been removed. In addition, the base-material temperature is set at 300° C. or less. This is because if the temperature exceeds 300° C., the base material is damaged with heat.

In the second aspect of the invention, the spray particle speed is set at less than 300 m/s. This is because if the spray particle speed is 300 m/s or more, the energy density of the spray frame increases at low pressure, causing a substantial increase in the base-material temperature. Furthermore, the base-material temperature is set at 600° C. or less. This is because if the base-material temperature exceeds 600° C., the topcoat layer is subjected to an abrupt heat cycle and damaged.

In the first and second inventions, another undercoat layer to be formed in a damaged portion of the undercoat layer may be formed of, for example, a Ni-based alloy in contrast to the Co-based alloy (Co-32% Ni-21% Cr-8% Al-0.5% Y) conventionally used. As another topcoat layer to be formed where the original topcoat layer has been removed, a material such as ZrO 2 —Dy 2 O 3 and ZrO 2 —Yb 2 O 3 may be used in contrast to the ZrO 2 .8Y 2 O 3 conventionally used.

In the first and second inventions, as a means for forming another undercoat layer where the original undercoat layer has been removed, for example, plasma spraying through a spray gun may be used. Furthermore, as a means for forming another topcoat layer where the original topcoat layer has been damaged, direct plasma spraying by the plasma spray gun or deposition by an electron beam physical vapor deposition method (EB•PVD method) may be used. If the EB•PVD method is employed, the durability of the topcoat layer can be improved more.

According to the present invention, after the damaged portion of the topcoat layer and the denatured portion of the undercoat layer corresponding to the damaged portion are removed, another undercoat layer is formed where the original undercoat layer has been removed, by spraying performed in the atmosphere at a spray particle speed of 300 m/s or more and a base-material temperature of 300° C. or less, and then, another topcoat layer is formed in the damaged portion of the original topcoat layer. Owing to this method, partial repair of the coat layer can be attained, thereby reducing the cost.

Furthermore, according to the present invention, after a damaged portion of the topcoat layer and the denatured portion of the undercoat layer corresponding to the damaged portion are removed, another undercoat layer is formed where the original undercoat layer has been removed by spraying at reduced pressure, a spray particle speed of less than 300 m/s, and a base-material temperature of 600° C. or less, and another topcoat layer is formed in the damaged portion of the topcoat layer. Owing to this method, partial repair of the coat layer can be attained, thereby reducing the cost.

Now, methods of repairing a Ni-based alloy part will be explained in accordance with individual embodiments of the present invention. The materials, numerical values and so forth described in the following embodiments are merely examples, which will not limit the scope of the present invention.

(Embodiment 1)

Referring to FIGS. 1A to 1D , explanation will be made.

As shown in FIG. 1A , an undercoat layer 12 composed of a Co-based material (e.g., Co-32% Ni-21% Cr-8% Al-0.5% Y), which has a denatured portion 12 a on its surface, is formed on a base material 11 . Also as shown in FIG. 1A , a topcoat layer 13 , which has a peeled-off portion (where the topcoat layer has been removed) 13 a and a damaged portion 13 b surrounding the peeled-off portion 13 a , is formed on the undercoat layer 12 . The topcoat layer 13 is composed of ZrO 2 .8Y 2 O 3 . From the structure in this state, the undercoat layer 12 present on the bottom of the peeled-off portion 13 a and the damaged portion 13 b of the topcoat layer 13 are selectively removed by grind-polishing to form an opening portion 14 (where the coat layers have been removed) in the undercoat layer 12 and the topcoat layer 13 (see FIG. 1B ). Note that reference numeral 12 ′ of FIG. 1B indicates the portion where the undercoat layer 12 has been removed, and reference numeral 13 ′ indicates the portion where the topcoat layer 13 has been removed.

Next, a masking material 15 having an opening corresponding to the opening portion 14 is arranged right upon the topcoat layer 13 and a plasma spray gun 16 is arranged right above the opening portion 14 . Subsequently, plasma spray is applied to the opening 14 in the atmosphere at a spray particle speed of 500 m/s and a base-material temperature of 150° C. to form a Co-based alloy layer, e.g., CoNiCrAlY layer 17 in the removed portion 12 ′ where the undercoat layer 12 has been removed. In this way, the repair of the undercoat layer 12 is completed (see FIG. 1C ). Furthermore, plasma spraying is applied to the opening portion 14 by means of the plasma spray gun 16 to form a topcoat layer 18 composed of ZrO 2 —Yb 2 O 3 in the removed portion 13 ′ where the topcoat layer 13 has been removed. In this way, the repair of the topcoat layer 13 is completed (see FIG. 1D ).

In Embodiment 1, the undercoat layer 12 present on the bottom of the peeled-off portion 13 a of the topcoat layer 13 and the damaged layer 13 b are selectively removed to form the opening portion 14 in the undercoat layer 12 and the topcoat layer 13 . Thereafter, plasma spraying is applied to the opening portion 14 right above it by means of the plasma spray gun 16 in the atmosphere at a thermal particle speed of 500 m/s and a base-material temperature of 150° C. or less. In this manner, the removed portion 12 ′ of the undercoat layer 12 and the removed portion 13 ′ of the topcoat layer 13 are sequentially repaired. Accordingly, since further coating of the entire rotor blade is not required as is in the art, the cost can be reduced.

Further in Embodiment 1, since a Ni-based alloy layer 17 is formed in the removed portion, where the undercoat layer 12 has been removed and exposed in the opening portion 14 , the durability can be improved compared to a conventional undercoat layer 12 . Furthermore, since the topcoat layer 18 composed of ZrO 2 —Yb 2 O 3 is formed in the removed portion 13 a where the topcoat layer 13 has been removed, the durability can be improved compared to a conventional topcoat layer 13 .

(Embodiment 2)

Referring to FIGS. 2A to 2D , explanation will be made. Like reference numerals are used to designate like structural elements corresponding to those like in FIGS. 1A to 1D and any further explanation is omitted for brevity's sake.

As shown in FIG. 2A , an undercoat layer 12 having a denatured portion 12 a is formed on a base material 11 . The undercoat layer 12 used herein is composed of a Ni-based material, for example, NiCoCrAlY. Furthermore, as shown in FIG. 2A , a topcoat layer 13 , which has a peeled-off portion (removed portion) 13 a and a damaged portion 13 b surrounding the removed portion 13 a , is formed on the undercoat layer 12 . The topcoat layer 13 is composed of ZrO 2 .8Y 2 O 3 .

From the structure in this state, the undercoat layer 12 present on the bottom of the peeled-off portion 13 a and the damaged portion 13 b of the topcoat layer 13 are selectively removed by grind-polishing, thereby forming an opening portion 14 in the undercoat layer 12 and the topcoat layer 13 (see FIG. 2B ).

Next, a masking material 15 having an opening corresponding to the opening portion 14 is arranged right upon the topcoat layer 13 and a plasma spray gun 16 is arranged right above the opening portion 14 . Subsequently, plasma spraying is applied to the opening 14 at reduced pressure, a spray particle speed of 200 m/s, and a base-material temperature of 150° C. to form a Ni-based alloy layer, an NiCoCrAlY layer 21 , in the removed portion 12 ′ where the undercoat layer 12 has been removed. In this way, the repair of the undercoat layer 12 is completed (see FIG. 2C ). Furthermore, spraying is applied to the opening portion 14 by means of a plasma spray gun 16 to form a topcoat layer 22 composed of ZrO 2 —Yb 2 O 3 in the removed portion 13 ′ where the topcoat layer has been removed. In this way, the repair of the topcoat layer 13 is completed (see FIG. 2D ).

According to Embodiment 2, the undercoat layer 12 present on the bottom of the peeled-off portion 13 a of the topcoat layer 13 and the damaged layer 13 b are selectively removed to form the opening portion 14 in the undercoat layer 12 and the topcoat layer 13 . Thereafter, plasma spraying is applied to the opening portion 14 from right above by means of the spray gun 16 at reduced pressure, a plasma spray particle speed of 500 m/s, and a base-material temperature of 150° C. or less. In this manner, the removed portion 12 ′ of the undercoat layer 12 and the removed portion 13 ′ of the topcoat layer 13 are sequentially repaired. Accordingly, since further coating of the entire rotor blade is not required as is in the art, the cost can be reduced.

Further in Embodiment 2, since a Ni-based alloy layer 21 is formed in the removed portion, where the undercoat layer 12 has been removed and exposed in the opening portion 14 , the durability can be improved compared to a conventional undercoat layer 12 . Furthermore, since the topcoat layer 22 composed of ZrO 2 —Yb 2 O 3 is formed in the removed portion 13 a where the topcoat layer 13 has been removed, the durability can be improved compared to a conventional topcoat layer 13 .

(Embodiment 3)

Referring to FIGS. 3A to 3D , explanation will be made. Like reference numerals are used to designate like structural elements corresponding to those like in FIGS. 1A to 1D and any further explanation is omitted for brevity's sake.

Similarly to Embodiment 1, as shown in FIG. 3A , an undercoat layer 12 , which has a denatured portion 12 a , is formed on a base material 11 and a topcoat layer 13 , which has a peeled-off portion (removed portion) 13 a and a damaged portion 13 b surrounding the removed portion 13 a , is formed on the undercoat layer 12 . The topcoat layer 13 is composed of ZrO 2 .8Y 2 O 3 . From the structure in this state, the undercoat layer 12 corresponding to the peeled-off portion 13 a and the damaged portion 13 b of the undercoat layer 12 are selectively removed by grind-polishing to thereby form an opening portion 14 in the undercoat layer 12 and the topcoat layer 13 (see FIG. 3B ).

Next, a masking material 15 having an opening corresponding to the opening portion 14 is arranged right upon the topcoat layer 13 and a plasma spray gun 16 is arranged right above the opening portion 14 . Subsequently, plasma spraying is applied to the opening 14 in the atmosphere at a spray particle speed of 500 m/s and a base-material temperature of 150° C. to form a Co-based alloy layer, a CoNiCrAlY layer 17 , in the removed portion 12 ′ of the undercoat layer 12 . In this way, the repair of the undercoat layer 12 is completed (see FIG. 3C ). Furthermore, after the masking material 15 and the plasma spray gun 16 are removed, a topcoat layer 23 composed of ZrO 2 —Yb 2 O 3 in the removed portion 13 ′ where the topcoat layer has been removed, was formed by the EB-PVD method. In this way, the repair of the topcoat layer 23 is completed (see FIG. 3D ).

According to Embodiment 3, similar to Embodiment 1, since further coating of the entire rotor blade is not required as is in the art, the durability of the undercoat layer 12 and the topcoat layer 23 can be improved. In addition, since the topcoat layer 23 is formed by the EB-PVD method, the durability of the top coat layer 23 can be further increased.